Apparatus and method for maintaining optical ferrule alignment during thermal expansion or contraction

ABSTRACT

An optical ferrule has a different thermal expansion coefficient than a substrate to which a optical device is mounted, the ferrule optically coupling the device to one or more optical fibers. The optical ferrule includes and/or a cradle in which the ferrule is mounted include lateral and longitudinal engagement feature that ensure alignment with the optical device at an operating temperature, the ferrule expanding relative to the substrate when transitioning to the operating temperature.

TECHNICAL FIELD

This disclosure relates generally to connector assemblies and methodsrelated to connector assemblies.

BACKGROUND

Optical connectors can be used for a variety of applications includingtelecommunications networks, local area networks, data center links, andinternal links in computer devices. Increasingly, optical functions arebeing incorporated in small integrated devices, such as photonicintegrated circuits (PIC). A PIC device may include optical elementssuch as waveguides, gratings detectors, lasers, etc., that arefabricated using processes such as material deposition,photolithography, and etching. A PIC may be coupled with externaloptical devices via optical fibers. One challenge in utilizing a PIC inthis way is efficient coupling of light between optical fibers andsmall-core PIC waveguides or other small-scale optical device on thePIC. Existing solutions involve active alignment of the fibers followedby permanent attachment to the devices, which is expensive, slow, andoften high loss.

BRIEF SUMMARY

One embodiment is directed to an optical ferrule having an attachmentarea for receiving and permanently attaching to a plurality of opticalfibers. A light redirecting member of the ferrule receives light, alonga first direction, from a plurality of fibers received by andpermanently attached to the attachment area and redirects the receivedlight along a different second direction. The redirected light exits theferrule at exit locations on a mating plane. The exit locations aresubstantially centered on a first alignment plane normal the firstdirection. A pair of first engagement features protrude from oppositelateral sides of the optical ferrule. The first engagement features aresubstantially centered on the first alignment plane. A second engagementfeature, different from the pair of first engagement features, protrudesfrom a front side of the optical ferrule and is substantially centeredon a second alignment plane perpendicular to the first alignment plane.The second alignment plane bisects the exit locations into substantiallyequal halves.

In some configurations, the exit locations may include a row of opticaloutput locations along the first alignment plane. The first engagementfeatures may include first and second tabs extending from the oppositelateral sides of the optical ferrule. The first and second tabs arelocated within respective first and second cavities of a cradle thatsecures the optical ferrule. The first and second cavities constrain thetwo tabs along the first direction when the optical ferrule is fit intothe cradle. In such a case, the optical ferrule may further comprisefirst and second lateral clearances between the first and second tabsand the respective first and second cavities such that the tab candisplace in a lateral direction, wherein there is little or no clearancebetween the first and second tabs and the respective first and secondcavities in the first direction.

In other configurations, the second engagement feature may comprise atab extending from the front side, the tab being placed in a cavity of acradle configured to secure the ferrule. In such a case, a clearance isincluded between the tab and the cavity such that the tab can displacein the first direction, wherein there is little or no clearance betweenthe first and second tabs and the respective first and second cavitiesin the lateral direction.

In some configuration, the optical ferrule may be formed of a polymer.The optical ferrule may further comprise a mating surface that opticallyinterfaces with an optical device on a substrate. The optical ferrulemay be configured to loosely fit into a cradle at an assemblytemperature and to tightly fit into the cradle at an operatingtemperature. In such a case, the assembly temperature may be lower thanthe operating temperature.

In another embodiment, an optical ferrule, comprises an attachment endconfigured to receive and secure an optical waveguide. A distal tip isopposed to the attachment end along a longitudinal direction. A lightredirecting element is configured to redirect light between the opticalwaveguide and a mating surface of the optical ferrule. A longitudinalconstraint member is operable to interface with a correspondinglongitudinal constraint member of a cradle that receives and secures theoptical ferrule. A side-to-side constraint member is operable tointerface with a corresponding side-to-side constraint member of thecradle. The longitudinal and side-to-side constraint members minimizedisplacement of a reference point of the optical ferrule relative to acorresponding reference point of the cradle due to different thermalexpansion coefficients of the optical ferrule and the cradle causing achange in size of the optical ferrule relative to the cradle in responseto a change of temperature.

In some configurations, the mating surface includes a row of opticaloutput locations along a side-to-side line, the reference point being ata center of the side-to-side line. The longitudinal constraint membermay comprise two tabs extending from opposing sides of the opticalferrule and aligned with the side-to-side line. Further, thecorresponding longitudinal constraint members of the cradle may comprisetwo cavities that respectively constrain the two tabs longitudinally andallow side-to-side displacement of the two tabs when the optical ferruleis fit into the cradle. The side-to-side constraint member may comprisea tab extending from the distal tip aligned with the center of theside-to-side line. Further, the corresponding side-to-side constraintmember may comprise a cavity that constrains side-to-side displacementof the tab and allows longitudinal displacement of the tab when theoptical ferrule is fit into the cradle.

In one configuration, a first thermal coefficient of expansion of theoptical ferrule is larger than a second thermal coefficient of expansionof the cradle. The optical ferrule may be formed of a polymer. Themating surface may be operable to optically interface with an opticaldevice on a substrate, wherein the cradle aligns the optical ferrulewith the optical device. The optical ferrule may be configured toloosely fit into the cradle at an assembly temperature and to tightlyfit into the cradle at an operating temperature, in which case theassembly temperature may be lower than the operating temperature.

In another embodiment, a cradle is configured to receive and secure anoptical ferrule. The cradle comprises a corresponding longitudinalconstraint member operable to interface with a longitudinal constraintmember of the optical ferrule. A corresponding side-to-side constraintmember is operable to interface with a side-to-side constraint member ofthe optical ferrule. The longitudinal and side-to-side constraintmembers minimize displacement of a reference point of a mating surfaceof the optical ferrule with a corresponding reference point of thecradle due to a change in size of the optical ferrule relative to thecradle. The change in size is induced by different thermal expansioncoefficients of the optical ferrule and the cradle and a change intemperature.

In some configurations, the mating surface may comprise a row of opticaloutput locations along a side-to-side line, the reference point being ata center of the side-to-side line. The longitudinal constraint member ofthe optical ferrule may comprise two tabs extending from opposing sidesof the optical ferrule and aligned with the side-to-side line. Further,the corresponding longitudinal constraint members of the cradle maycomprise two cavities that respectively constrain the two tabs and allowside-to-side displacement of the two tabs when the optical ferrule isfit into the cradle. The side-to-side constraint member may comprise atab extending from a distal tip of the optical ferrule that is alignedwith the center of the side-to-side line and the correspondingside-to-side constraint member may comprise a cavity that constrainsside-to-side displacement of the tab and allows longitudinaldisplacement of the tab when the optical ferrule is fit into the cradle.

In some configurations, a first thermal coefficient of expansion of theoptical ferrule is larger than a second thermal coefficient of expansionof the cradle. The cradle is formed of a silica or other ceramic, or alow thermal expansion metal alloy such as Invar or Covar. The cradle mayalign and secure the optical ferrule to a substrate such that the matingsurface optically interfaces with an optical device on the substrate.The optical ferrule may be configured to loosely fit into the cradle atan assembly temperature and to tightly fit into the cradle at anoperating temperature, and the assembly temperature may be lower thanthe operating temperature.

In some configurations, the cradle may further comprise a lensconfigured to modify a light path between the optical ferrule and anoptical device, the optical device located on a substrate to which thecradle is attached. The lens may comprise a collimating lens. The cradlemay further comprise second corresponding longitudinal and side-to-sideconstraint members configured to minimize a second displacement of asecond reference point of a second optical ferrule with a correspondingsecond reference point of the cradle due to a change in size of thesecond optical ferrule relative to the cradle. In another embodiment, anoptical assembly, comprises an optical ferrule comprising a lightredirecting element configured to redirect light between an opticalwaveguide and a mating surface of the optical ferrule. The opticalferrule has a first thermal expansion coefficient. A cradle isconfigured to hold and secure the optical ferrule to a substrate. Thecradle has a second thermal expansion coefficient different than thefirst thermal expansion coefficient. The optical ferrule is configuredto fit loosely within the cradle at an assembly temperature and toexpand into the cradle at an operating temperature.

In some configurations, the optical ferrule may comprise at least oneconstraint member and the cradle may comprise at least one correspondingconstraint member. The constraint member and corresponding constraintmember interface such that a displacement between a reference point ofthe optical ferrule and a corresponding reference point of the cradle isminimized between the assembly temperature and the operatingtemperature. The optical ferrule may comprise a row of optical outputlocations arranged in a side-to-side line along the mating surface, thereference point being at a center of the side-to-side line. The at leastone constraint member may comprise a longitudinal constraint member anda side-to-side constraint member, and the at least one correspondingconstraint member may comprise a corresponding longitudinal constraintmember that interfaces with the longitudinal constraint member and acorresponding side-to-side constraint member that interfaces with theside-to-side longitudinal constraint member. The optical assembly mayfurther comprise a side-to-side clearance between the longitudinalconstraint member and the corresponding longitudinal constraint membersuch that the longitudinal constraint member can displace in aside-to-side direction, and wherein there is little or no clearancebetween the longitudinal constraint member and the correspondinglongitudinal constraint member in a longitudinal direction.

In some configurations, the assembly temperature may be lower than theoperating temperature. The optical ferrule may be formed of a polymerand the cradle may be formed of a ceramic. The optical assembly mayfurther comprise an optical device attached to the substrate, the cradlealigning one or more optical output locations of the optical ferrulewith the optical device. At least part of the one or more optical outputlocations may be misaligned with the optical device at the assemblytemperature and the one or more optical output locations may beoptimally aligned with the optical device at the operating temperature.The cradle further may comprise a lens configured to modify a light pathbetween the optical ferrule and an optical device, the optical devicelocated on the substrate. The lens may comprise a collimating lens. Thecradle may be further configured to hold and secure a second opticalferrule to a substrate, the second optical ferrule being is locatedlaterally to the optical ferrule. The cradle and the optical ferrule maybe formed integrally.

In another embodiment, a method involves coupling an optical ferrule toa substrate via a cradle at an assembly temperature. The optical ferrulefits loosely within the cradle at the assembly temperature. The opticalferrule has a first thermal expansion coefficient and the cradle has asecond thermal expansion coefficient different than the first thermalexpansion coefficient. One or more devices are coupled to the substratesuch that the substrate, the cradle, and the optical ferrule reach anoperating temperature. A relative expansion of the optical ferrule andthe cradle at the operating temperature cause the one or more outputlocations of the optical ferrule to be aligned with an optical deviceattached to the substrate.

In some configurations, the relative expansion of the optical ferruleand the cradle at the operating temperature causes the optical ferruleto fit tightly within the cradle. The method may further comprisetransferring light between the optical ferrule and the optical devicevia the one or more output locations at a mating surface of the opticalferrule at the operating temperature. Transferring light between theoptical ferrule and the optical device may comprise redirecting lightbetween the mating surface and an optical waveguide coupled to an end ofthe optical ferrule. The method may further comprise minimizing adisplacement between a reference point of the optical ferrule and acorresponding reference point of the cradle between the assemblytemperature and the operating temperature. The displacement may beminimized via at least one longitudinal constraint member of the opticalferrule that interfaces with at least one corresponding longitudinalconstraint member of the cradle and at least one side-to-side constraintmember of the optical ferrule that interfaces with at least onecorresponding side-to-side constraint member of the cradle.

In another embodiment, a cradle is configured to receive and secure anoptical ferrule, the cradle comprises a restraining member configured torestrain the optical ferrule. Two or more bonding pads are usable with abonding material that bonds the cradle to a substrate at a bondingtemperature. The cradle has a first thermal expansion coefficient andthe substrate having a second thermal expansion coefficient differentthan the first thermal expansion coefficient. Two or more mountingmembers mechanically couple the respective two or more bonding pads tothe cradle. The two or more mounting members reversibly deflect inresponse to a force applied between the bonding pad and attachmentregions of the two or more mounting members to the cradle. The force isdue to the different first and second expansion coefficients.

In some configurations, the two or more mounting members may comprisetwo or more legs affixed near a top surface of the cradle that isopposed to the two more bonding pads. The two or more legs may comprisefour or more legs each affixed at a different corner of the cradle. Thetwo or more legs may comprise three or more legs each affixed at adifferent edge of the cradle. The two or more mounting members maycomprise two or more hollow cylinders or hollow prisms that extend froma bottom surface of the cradle that faces the substrate. The two or moremounting members may be symmetrically arranged relative to the cradlesuch that the reversible deflection minimizes displacement of areference point of the optical ferrule relative to a correspondingreference point of the substrate. The displacement may be minimized whenthe cradle expands or contracts relative to the substrate due to achange in temperature.

In some configurations, the cradle may further comprise a lensconfigured to modify a light path between the optical ferrule and anoptical device, the optical device located on a substrate to which thecradle is attached. The lens may comprise a collimating lens.

In another embodiment, a cradle is configured to receive and secure anoptical ferrule. The cradle comprises a restraining member configured torestrain the optical ferrule and two or more bonding pads with a bondingmaterial that bonds the cradle to a substrate at the bondingtemperature. The cradle has a first thermal expansion coefficient andthe substrate has a second thermal expansion coefficient different thanthe first thermal expansion coefficient. Two or more mounting membersmechanically couple the respective two or more bonding pads to thecradle. The two or more mounting members are deformable in response toexpansions of the cradle relative to the substrate. The relative changein expansions are due to a change between a bonding temperature and anoperating temperature. The two or more mounting members are deformablesuch that the cradle maintains an alignment between the optical ferruleand an optical device attached to the substrate at least at theoperating temperature.

In some configurations, the two or more mounting members may comprisetwo or more legs affixed near a top surface of the cradle that isopposed to the two more bonding pads. The two or more legs may comprisefour or more legs each affixed at a different corner of the cradle. Thetwo or more legs may comprise three or more legs each affixed at adifferent edge of the cradle. The two or more mounting members maycomprise two or more hollow cylinders or hollow prisms that extend awayfrom a bottom surface of the cradle that faces the substrate. The two ormore mounting members may be symmetrically arranged relative to thecradle such that the reversible deflection minimizes displacement of areference point of the optical ferrule relative to a correspondingreference point of the substrate. The displacement may be minimized whenthe cradle expands or contracts relative to the substrate due to achange in temperature. In some configurations, the cradle may furthercomprise a lens configured to modify a light path between the opticalferrule and the optical device. The lens may comprise a collimatinglens.

In another embodiment, method involves bonding two or more bonding padsof a cradle to a substrate at a bonding temperature. The cradlecomprises two or more mounting members that mechanically couple therespective two or more bonding pads to the cradle. The cradle andsubstrate reach an assembly temperature. The difference between thebonding temperature and the assembly temperature causes a deformation ofthe mounting members due to a difference in thermal expansioncoefficients between the cradle and the substrate. An optical ferrule isinserted into the cradle such that the cradle secures the opticalferrule relative to an optical device mounted on the substrate.

In some configurations, the method may further comprise activating oneor more devices coupled to the substrate such that the substrate, thecradle, and the optical ferrule reach an operating temperature, whereinexpansion of the cradle relative to the substrate at the operatingtemperature brings the optical ferrule into alignment with the opticaldevice. The method may further comprise transferring light between theoptical ferrule and the optical device via the one or more outputlocations at a mating surface of the optical ferrule at the operatingtemperature. Transferring light between the optical ferrule and theoptical device may comprise redirecting light between the mating surfaceand an optical waveguide coupled to an end of the optical ferrule.

In another embodiment, an optical component includes an attachment areafor receiving and permanently attaching a plurality of optical fibers. Alight redirecting member receives light along a first direction from theplurality of optical fibers and redirects the light along a differentsecond direction. The redirected light exits the optical component atexit locations on a mating plane. The exit locations are substantiallycentered on a first alignment plane normal to the first direction. Twoor more bonding pads of the component are usable with a bonding materialthat bonds the optical component to a substrate at a bondingtemperature. The optical component has a first thermal expansioncoefficient and the substrate has a second thermal expansion coefficientdifferent than the first thermal expansion coefficient. Two or moremounting members mechanically couple the respective two or more bondingpads to the optical component. The two or more mounting membersreversibly deflect in response to a force applied between the bondingpad and attachment regions of the two or more mounting members to theoptical component, such that the location of the intersection of thefirst alignment plane with the substrate is minimally affected bytemperature. In one configuration, the optical component may furtherinclude a lens configured to modify a light path between the componentand an optical device, the optical device located on the substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1, 2, and 3 are cross-sectional and top views of an opticalferrule and cradle in accordance with some embodiments;

FIG. 4 is a perspective view of an optical ferrule according to anexample embodiment;

FIG. 5 is a perspective, exploded, view of an optical connector systemaccording to an example embodiment;

FIGS. 6 and 7 are perspective and top views of the optical connectorsystem of FIG. 5;

FIGS. 8 and 9 are top views of an optical ferule and cradle inaccordance with other embodiments;

FIG. 10 is a perspective, exploded, view of an optical connector systemaccording to an example embodiment;

FIG. 11 is a perspective view of the optical connector system of FIG.10;

FIG. 12 is a perspective view of a cradle used in the optical connectorsystem of FIG. 10;

FIG. 13 is a perspective view of a cradle according to another exampleembodiment;

FIGS. 14A and 14B are bottom and side views of a cradle according toanother example embodiment;

FIGS. 15 and 16 are diagrams of optical input/output locations of anoptical ferrule according to example embodiments;

FIGS. 17 and 18 are flowcharts of methods according to exampleembodiments;

FIG. 19 is a side view of an optical ferrule and cradle in accordancewith some embodiments;

FIG. 20 is a top view of multiple optical ferrules and a cradle inaccordance with some embodiments; and

FIG. 21 is a side view of an optical component according to an exampleembodiment.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments described herein relate to optical cable subassemblies,optical connectors, and packages for photonic integrated circuits(PICs). Connector interfaces are described that can mate one or morefiber optic waveguides to corresponding optical devices that are mountedon or integral with a substrate. In some cases, the optical device andsubstrate may be formed integrally as part of a PIC. In other cases, theoptical device may be mounted (e.g., bonded, soldered) to a circuitboard, such that the circuit board acts as a substrate. In other cases,the optical device may be mounted on an interposer or other carrier,that is in turn mounted on a circuit board. In either case, the opticaldevices may include waveguides, gratings, detectors, modulators, lightsources (e.g., lasers) and may include other integrated optical featuressuch as lenses, collimators, mirrors, filters, etc.

The optical connectors described below may include ferrules attached tomultiple parallel waveguides (e.g., 4, 8 or 12 or more parallelwaveguides). The individual waveguides are typically optical fibers madeof glass (e.g., single-mode or multi-mode fibers) with a protectivebuffer coating, and the parallel buffered fibers are enclosed by ajacket to form a ribbon. The ferrule may include a light redirectingelement that redirects light (e.g., by an angle near 90 degrees) fromthe optical waveguide to a mating surface where the light is directedthrough an output window. The optical ferrule may be configured toexpand the beam that exits the mating surface, which allows fornon-contact optical coupling and can relax the connector-to-connectormechanical alignment precision when compared with other types of opticalconnectors, such as physical contact connectors.

The optical ferrule may be made of a polymer having desirable opticalproperties that can be mass produced, e.g., through injection molding.An optics-grade polymer such as Zeonex K26R may have a coefficient ofthermal expansion (CTE) (also referred to herein as ‘thermal expansioncoefficient’) on the order of 63 ppm/° C. In contrast, the substrate towhich the optical ferrule is mated is may be formed from a material suchas a silicon which has a CTE on the order of 2.6 ppm/° C. Thisdifference in CTE can complicate aligning the optical ferrule to asubstrate-mounted or substrate-integrated optics device. For example,assembly of the optical ferrule to the substrate may occur at roomtemperature, but the optical device (and any other devices thermallycoupled to the substrate) may cause the assembly to run at asignificantly higher temperature than room temperature. The substrateand optical ferrule will expand or contract by different amounts atthose different temperatures due to CTEs.

The difference in expansion between the substrate and the opticalferrule can result in the optical beams being out of alignment at somerange of temperatures. Because the maximum optical coupling between theoptical ferrule and optical device is needed at the operatingtemperature of the device, the optical ferrule is sized such that itexpands to the desired size at operating temperature. At the operatingtemperature, the light beams entering or exiting the optical ferruleshould be spaced substantially the same as elements on the device thatcouple to the light beams. However, the assembly of the optical ferrule,substrate, and device, will generally occur at a different temperature(e.g., a lower temperature) than the operating temperature. At thislower temperature, at least some of the optical output locations of theferrule may be expected to be misaligned. Thus the system will havefeatures to ensure the ferrule comes into correct alignment duringoperation. Further, the assembled system can be expected to cyclebetween operating temperatures and room temperature during service,e.g., when the optical device is powered up and down. This will resultin the repeated expansion and contraction of the optical connectorrelative to the substrate and optical device. This may cause movementtherebetween, resulting in misalignment of the light beams.

In order to ensure that an optical ferrule with different CTE than adevice to which it is coupled maintains alignment even when subject to arange of temperatures, two approaches are described below. In bothapproaches, a cradle is used that receives the optical ferrule andsecures it to the substrate. In one approach, the cradle is made of amaterial with CTE similar to that of the substrate. The cradle andoptical ferrule include features that ensure the ferrule aligns with thesubstrate at an operating temperature range. In another approach, thecradle and ferrule are made of similar-CTE materials. In this approach,the cradle will be tightly attached to the ferrule over a wide range oftemperatures. The cradle, which will expand differently than thesubstrate, includes features that ensure the cradle aligns with thesubstrate at operating temperature, which will in turn align theferrule.

In FIGS. 1 and 2, simplified diagrams illustrate side andcross-sectional views of an optical ferrule 100 and cradle 102 accordingto an example embodiment. In this embodiment, the optical ferrule 100and cradle 102 are made of materials with different CTE. In thisspecific example, it is assumed that the thermal expansion coefficientof the ferrule is higher than that of the cradle. The optical ferrule100 includes an attachment end 101 configured to receive and secure anoptical waveguide 106 (in this example, a plurality of optical fibers asseen in FIG. 2). The interface between the waveguides 106 and theferrule 100 is generally referred to as an attachment area 103 thatreceives and permanently attaches the plurality of optical fibers 106. Adistal tip 104 of the optical ferrule 100 is opposed to the attachmentend 101 along a longitudinal direction 116. Note that in this and otherembodiments, the term “longitudinal” generally relates to theorientation of the elongated waveguides/fibers 106 at the attachment end101, and is not meant to be limiting as to the relative shape ordimensions of the optical ferrule 100.

The optical ferrule 100 includes a light redirecting member 108 thatreceives light 109 along a first direction (the longitudinal direction116) from the plurality of fibers 106. The light redirecting member 108redirects the received light along a different, second, direction 115,which in this example is normal to a substrate 120 to which the cradle102 is attached. Note that the light redirecting member 108 may work inthe other way, receiving light in direction 115 and sending it throughthe fibers 106 along direction 116. It will be understood that anydescription herein of light exiting or output from a ferrule is equallyapplicable to light entering or being input to the ferrule, and suchterms are not meant to limit how the ferrule and optical device mayinteract.

As best seen in FIG. 2, the redirected light 109 exits the opticalferrule at exit locations on a mating plane 117 (see exit locations 210in FIG. 2, also referred to herein as optical output-locations). Thismating plane 117 corresponds to a mating surface 110 of the ferrule 100in this example. The optical exit locations 210 are substantiallycentered on an alignment plane 119 normal to the first direction 116.

In FIG. 1, the ferrule 100 is shown separated from the cradle 102. Thecradle 102 is configured to receive and secure the optical ferrule 100as the ferrule 100 is moved downward in first direction 116. Forexample, the cradle 102 may include surfaces 114 onto or next to whichthe ferrule 100 is placed and is at least partially constrained.Additional constraints may be provided by a cap (not shown) that trapsthe ferrule 100 into the cradle 102.

Generally, at an assembly temperature, the ferrule 100 can fit looselywithin the cradle 102, e.g., such that minimal force is needed to insertthe ferrule 100 within the cradle 102. At the operating temperature, theferrule 100 will have expanded more than the cradle 102, resulting in atight fit. The tight fit at the operating temperature is at least suchthat deflections caused by external forces, e.g., forces acting on theoptical waveguides 106, will not cause excessive optical misalignment ofbeams coupled between the ferrule 100 and an optical device 122. Thetight fit may involve contact or interference between at least part ofthe ferrule 100 and cradle 102, but may also have some gaps therebetweenin at least some regions. The cradle 102 is made from a material such aceramic (e.g., silica) or metal alloy that has a similar CTE as thesubstrate 120, and so there will be minimal relative expansiontherebetween due to the same temperature changes.

In FIG. 2, the optical ferrule 100 and cradle 102 are shown in theloose-fitting configuration, e.g., at the assembly temperature. Alsoseen in this view is a longitudinal constraint member 200 operable tointerface with a corresponding longitudinal constraint member 202 of thecradle 102. In this example, the longitudinal constraint member 200 isconfigured as a pair of first engagement features (e.g., tabs)protruding from opposite lateral sides of the optical ferrule 100 in aside-to-side direction 208. The engagement features 200 aresubstantially centered on the alignment plane 119. The correspondinglongitudinal constraint member 202 is configured in this example as apair of cavities that encompass the engagement features 200. Note theside-to-side clearances 203 between the longitudinal constraint member200 and the corresponding longitudinal constraint members 202 such thatthe longitudinal constraint member 200 can displace in the side-to-sidedirection 208 (e.g., due to expansion of the ferrule 100), however thereis little or no clearance therebetween in the longitudinal direction116.

The optical ferrule 100 includes a side-to-side constraint member 204operable to interface with a corresponding side-to-side constraintmember 206 of the cradle 202. In this example, the side-to-sideconstraint member 204 is configured as a second engagement feature,different from the pair of first engagement features 200, protrudingfrom a front side (distal end 104) of the optical ferrule 100. A secondalignment plane 214 passes through the second engagement feature 204 andis perpendicular to the alignment plane 119 and substantially bisectsexit locations 210 into substantially equal halves. A longitudinalclearance 205 between longitudinal constraint member 200 and thecorresponding longitudinal constraint member 204 is such that thelongitudinal constraint member 200 can displace in the longitudinaldirection 116 (e.g., due to expansion of the ferrule 100), however thereis little or no clearance therebetween in the side-to-side direction208.

The exit locations 210 are a feature of the ferrule 100, e.g., geometriclocations defined by the shape and location of the light redirectingmember and correspond to locations of light beams coupled into or out ofthe ferrule 100. In this view (at the assembly temperature) the pitch ofthe exit locations 210 will be different than those of correspondingoptical features (not shown) of the optical device 122. The pitch ofexit locations 210 will approximately equal that of the correspondingoptical features of the optical device 122 at the operating temperature.

The longitudinal and side-to-side constraint members 200, 204 areconfigured to align the exit locations 210 with the correspondingoptical features of the optical device 122 at the operating temperature.This can be done by minimizing displacement of a reference point 212 ofthe optical ferrule 100 relative to a corresponding reference point 215of the cradle 102 due to a change in size of the optical ferrule 100relative to the cradle 102 caused by a change of temperature. In FIG. 3,the optical ferrule 100 is shown in the cradle 102 at or near andoperating temperature. The optical ferrule 100 has expanded more thanthe cradle 102 due to its larger CTE, such that the ferrule 100 now fitstightly within the cradle 102, e.g., fills the cavity within the cradle102. Due to the arrangement of the constraint members 200, 204 relativeto the planes 119, 214, displacement between reference points 212, 215is minimized, resulting in the exit locations 210 being substantiallyaligned with the optical device 122. The exit locations 210 haveexpanded in the side-to-side direction 208 such that a pitch of the exitlocations 210 also matches that of the optical device 122.

Note that more than the indicated constraint members may be used. Asindicated by the dashed box 300, an additional side-to-side constraintmay supplement 204 and 206. Alternatively. as indicated by the dashedboxes 301 and 302, other side-to-side constraint members may be usedinstead of to side-to-side constraint member 204 and 206. Similarlongitudinal restraint members may be used as well. In someconfigurations, constraint members may be located elsewhere or inaddition to sides of the ferrule. This is seen in the example embodimentshown in the perspective view of FIG. 4. In this view, a mating surface402 of the ferrule 400 is seen, as is an exit window 404 in which can beseen optical input/output locations 406. A longitudinal constraintmember includes ridges 408 and a side-to-side constraint member includesridges 410. A cradle (not shown) would include corresponding channelsinto which the ridges 408, 410 would fit. Any combination of ridges 408,410 shown in FIG. 4 and tabs 202, 204 shown in FIG. 2 may be used inother embodiments.

Note that in the above embodiments it was assumed that the CTE of theoptical ferrule is greater than that of the cradle and substrate, andthat the assembly temperature is less than the operating temperature.However, in this and other embodiments, a system with inversecharacteristics (CTE of the optical ferrule is less than that of thecradle and substrate, and that the assembly temperature is greater thanthat of the operating temperature) may also achieve a similar result,with a tight fit between the cradle and ferrule at operating temperatureand a loose fit therebetween at assembly temperature by providingconstraint members in the cradle that fit into cavities in the ferrule.

In FIG. 5, a perspective exploded view shows an optical connectingarrangement according to another example embodiment. An optical ferrule500 and cradle 502 are made of materials with different CTE. The opticalferrule 500 includes an attachment area 503 that receives andpermanently attaches an optical fiber ribbon 506. A distal tip 504 ofthe optical ferrule 500 is opposed to the attachment area 503 along alongitudinal direction 516. The ferrule 500 includes a light redirectingmember 508 that redirects light 509 between the optical fiber ribbon 506in direction 516 and an optical device 522 in direction 515, which isnormal to a substrate 520 to which the cradle 502 is attached. In otherembodiments, the redirected direction 515 may be non-normal to thesubstrate. The redirected light 509 exits and enters the optical ferrule500 at exit locations (not shown) on a mating plane 517, whichcorresponds to a mating surface (not shown) of the ferrule 500. Theoptical exit locations are substantially centered on an alignment plane519 normal to the first direction 516. Antireflection coatings may beused to reduce reflections of light entering or exiting the ferrule.Note that the cradle 502 includes a void 511 which facilitates passingthe light 509 between the ferrule 500 and optical device 522.

In FIG. 5, the ferrule 500 is shown separated from the cradle 502. Thecradle 502 is configured to receive and secure the optical ferrule 500as the ferrule 500 is moved downward in first direction 515. Forexample, the cradle 502 includes surfaces 514 onto or next to which theferrule 100 is placed and is at least partially constrained. Additionalconstraints may be provided by a cover 522 that traps the ferrule 500into the cradle 502. The illustrated cover 522 is held in place byscrews 524 that fasten to nuts 526. Note that other attachment meanssuch as clips or bonding may be used to secure the cover 522 to thecradle 502 and substrate 520.

The cradle 502 may be permanently attached to the substrate 520 beforeassembly of the ferrule 500 with the cradle 502. As indicated by pads518, this attachment may include soldering or other types of bonding. Inthe case of solder bonding, the pads would be metal wetted by thesolder. The cradle 502 can be precisely placed over the optical device522, e.g., via a pick and place machine, and then secured to thesubstrate 520 through the application of heat, light cure adhesives,etc. Thereafter, the cradle 502 and substrate 520 form a subassembly towhich the ferrule 500 and fiber optic ribbon 506 may be attached, e.g.,at room temperature manually or via a robotic device. The finalassembly, which includes attachment of the cover 522, can be seen in theperspective view of FIG. 6. Note that, as seen in FIG. 6, the distal tip514 extends outside the cradle 502. The tip 514 corresponds to a moldinggate in this design, so by having the tip 514 extend outside the cradle502, any degating vestige does not affect alignment.

Generally, at an assembly temperature, the ferrule 500 can fit looselywithin the cradle 502 such that minimal force is needed to insert theferrule 500 within the cradle 502. This is seen in the top view of FIG.7, where gaps 700 can be seen between the outline of the ferrule 500 andthe receiving cavity of the cradle 502. At an operating temperaturehigher than the assembly temperature, the ferrule 500 will have expandedmore than the cradle 502, resulting in a tight fit, e.g., aninterference fit.

In reference again to FIG. 5, a longitudinal constraint member (tabs530) of the ferrule 500 is operable to interface with a correspondinglongitudinal constraint member (cavities 532) of the cradle 502. Theengagement tabs 530 are substantially centered on an alignment plane519, which defines a center of the optical output locations in direction526. The optical ferrule 100 includes a side-to-side constraint member(tab 534) operable to interface with a corresponding side-to-sideconstraint member (cavity 536) of the cradle 202. A plane 514 passesthrough the side-to-side constraint member 534 and is perpendicular tothe alignment plane 519 and substantially bisects the exit/entrancelocations of the light redirection member 508 into substantially equalhalves.

In another example embodiment shown in FIG. 20, a cradle 2002 isconfigured to receive and secure two or more ferrules 2000. The ferrules2000 may include features similar to those previously described, e.g.,ferrule 100 in FIG. 1. The ferrules 2000 and cradle 2002 have differentCTEs. The ferrules 2000 are offset from one another and are configuredto optically couple to devices 2006 on substrate 2008. The cradle 2002may be made of materials previously described above (e.g., ceramics,silica) and maintains alignment between the ferrules 2000 and thedevices 2006 in a transition from an assembly temperature to anoperating temperature. The cradle 2006 includes multiple correspondinglongitudinal 2010 and side-to-side 2012 constraint members configured tominimize multiple displacements between multiple reference points 2014of the multiple optical ferrules 2000 with multiple second referencepoints 2015 of the cradle 2006 due to a change in size of the multipleoptical ferrules 2000 relative to the cradle 2002.

In FIG. 8, a top view shows an optical ferrule 800 and cradle 802according to other example embodiments. In this example, the opticalferrule 800 and cradle 802 have the same or similar CTE, and these CTEare different than a CTE of a substrate 820 and optical device 822 towhich the ferrule 800 is mated. The optical ferrule 800 includes a lightredirection member 808 and an attachment area 803 that receives andpermanently attaches an optical fiber ribbon 806. A distal tip 804 ofthe optical ferrule 800 is opposed to the attachment area 803 along alongitudinal direction 816.

Because the optical ferrule 800 and cradle 802 have same or similar CTE,they can have a relatively tight fit at the assembly temperature. Thecomponents may be configured with a restraining member 801 such thatassembly and disassembly of the optical ferrule 800 and cradle 802 canbe done by hand, e.g., without significant installation forces, yetstill having features such as snaps, springs, etc., that ensure a tightfit to restrain the ferrule 800. In this example, the restraining member801 includes at least a perimeter surface of a cavity of the cradle 802,the shape of the perimeter surface matching the top view outline of theferrule 800. There may be small gaps between the restraining member 801surfaces and lateral surfaces of the ferrule 800 to aid in assembly ofthe ferrule. Other components, such as a cover may also restrain theferrule 800 after it is placed in the cradle 802. In other embodiments,the ferrule 800 may be formed integrally with the cradle 802, e.g.,molded as one piece.

Before assembly of the optical ferrule 800 to the cradle 802 (if thecomponents are formed separately), the cradle 802 will be attached tothe substrate 820. This may involve a high temperature process such assoldering. Thus the cradle includes two or more bonding pads 826 usablewith a bonding material (e.g., solder) that bonds the cradle to asubstrate at a bonding temperature. The bonding pads 826 representattachment points between the cradle 802 and the substrate 820, and thesubstrate 820 may have similar pads (not shown). This bondingtemperature is different than the assembly temperature (temperature whenthe ferrule 800 is inserted into the cradle 802), and may also bedifferent (e.g., higher than) the operating temperature of the assembly.Because these temperature differentials will result in greaterdimensional change in the cradle 802 than in the substrate 820, thecradle 802 includes two or more mounting members 828 with controlledcompliance that mechanically couple the respective two or more bondingpads 826 to the cradle 802.

In this diagram, the two or more mounting members 828 are schematicallyrepresented as springs at the corners of the cradle 802. The two or moremounting members 828 reversibly deflect in response to a force appliedbetween the bonding pad 826 and attachment regions 830 of the two ormore mounting members 828 to the cradle 802. Generally, these forces aredue to the different expansion coefficients of the cradle 802 andsubstrate 820, but may also be due to other forces, e.g., forces actingon the optical fibers 806. The stiffness of the mounting members 828 canbe selected so that they are sufficiently rigid to prevent excessivemovement in response to expected forces in use, while sufficientlyflexible to allow the cradle 802 to shrink and grow relative to thesubstrate 820 without breakage or other damage.

The mounting members 828 are configured such that forces acting on thecradle 802 via the mounting members 828 due to thermal expansion orcontraction of the cradle 802 relative to the substrate minimizes amisalignment between the cradle 802 and the optical device 822 in atleast one region. An example of this is shown in the simplified view ofFIG. 9. The cradle 802 and ferrule 800 are shown in an expandedconfiguration (e.g., at the bonding temperature) using solid lines, andshown in a contracted configuration (e.g., at the assembly temperature)using dashed lines. Note that the ferrule 800 would not typically belocated in the cradle 802 during bonding, but is shown to illustrate theeffects that expansion/contraction of the cradle 802 will have onalignment of the ferrule 800 with the optical device 822. A similarexpansion/contraction may occur between the assembly temperature and theoperating temperature, and the ferrule 800 would be located in thecradle 802 in that case. As indicated by dashed shapes 840, the mountingmembers and associated pads may include three or more mounting memberseach affixed at a different edge of the cradle 802.

A row of optical output locations 900 associated with the ferrule 800are shown in both the expanded and contracted configurations. Theseoutput locations 900 will align with optical features (e.g., facets,lenses, waveguides, detectors) of the optical device. In order tominimize the net displacement of these output locations 900 duringoperation, the mounting members 828 minimize a misalignment between areference point of the cradle 802 and a corresponding reference point ofthe optical device 822 and/or substrate 820 when the cradle 802 expandsor contracts due to temperature changes. In this figure, the centers ofcircles 902, 904 will define the reference point and correspondingreference point in this example.

In FIG. 10, a perspective exploded view shows an optical connectingarrangement according to another example embodiment. An optical ferrule1000 and cradle 1002 are made of materials with the same or similar CTE.The optical ferrule 1000 includes an attachment area 1003 that receivesand permanently attaches an optical fiber ribbon 1006. A distal tip 1004of the optical ferrule 1000 is opposed to the attachment area 1003 alonga longitudinal direction 1016. The ferrule 1000 includes a lightredirecting member 1008 that redirects light between the optical fiberribbon 1006 in direction 1016 and an optical device 1022 in direction1015, which is directed towards to a substrate 1020 to which the cradle1002 is attached. The redirected light 1009 exits and enters the opticalferrule 1000 at exit locations (not shown) on a mating plane 1017, whichcorresponds to a mating surface (not shown) of the ferrule 1000. Theoptical exit locations are substantially centered on an alignment plane1019 normal to the first direction 1016. Note that the cradle 1002includes a void 1011 which facilitates passing the light 1009 betweenthe ferrule 1000 and optical device 1022.

In FIG. 10, the ferrule 1000 is shown separated from the cradle 1002.The cradle 1002 is configured to receive and secure the optical ferrule1000 as the ferrule 1000 is moved downward in first direction 1015. Forexample, the cradle 1002 includes surfaces 1014 onto or next to whichthe ferrule 100 is placed and is at least partially constrained.Additional constraints may be provided by a cover 1022 that traps theferrule 1000 into the cradle 1002. The illustrated cover 1022 is held inplace by screws 1024 that fasten to nuts trapped in recesses 1206 in thecradle. Note that other attachment means such as clips or bonding may beused to secure the cover 1022 to the cradle 1002 and substrate 1020.

The cradle 1002 may be permanently attached to the substrate 1020 beforeassembly of the ferrule 1000 with the cradle 1002. As indicated by pads1018, this attachment may include soldering or other types of bonding.The bonding pads 1018 are usable with a bonding material that bonds thecradle 1002 to the substrate 1020 at the bonding temperature. The cradle1002 can be precisely placed over the optical device 1022, e.g., via apick and place machine, and then secured to the substrate 1020 throughthe application of heat, light-cured adhesive, etc. Thereafter, thecradle 1002 and substrate 1020 form a subassembly to which the ferrule1000 and fiber optic ribbon 1006 may be attached, e.g., at roomtemperature manually or via a robotic device. The final assembly, whichincludes attachment of the cover 1022, can be seen in the perspectiveview of FIG. 11.

The cradle 1002 includes two or more mounting members, which in thisexample are configured as legs 1032 affixed near a top surface 1030 ofthe cradle that is opposed to two more bonding pads (see bonding pads1200 in FIG. 12) of the cradle 1002. The cradle 1002 has a first thermalexpansion coefficient and the substrate 1020 has a second thermalexpansion coefficient different than the first thermal expansioncoefficient. Due to these differences in thermal expansion coefficient,the cradle 1002 will expand or contract relative to the substrate 1020at different temperatures. As seen in the perspective view of FIG. 12,the legs 1032 can deflect as indicated by the dashed lines. The legs1032 can also deflect in the other direction, due to gaps 1201 betweenthe legs 1032 and the body of the cradle 1002. In other embodiments,three or more legs may be each affixed at a different edge of the cradle1002 instead of or in addition to the corner legs (see mounting members840 in FIG. 8).

The legs 1032 are located around the perimeter of the cradle 1002, andall have the same dimensions. When the legs 1032 flex due to thermalexpansion, a reference point 1202 of the cradle 1002 will experienceminimum deflection relative to a corresponding reference point (seepoint 1034 in FIG. 10) of the optical device 1022. Thus the legs 1032will be arranged symmetrically around the reference point 1202, whichmay be different than a center point of the cradle. Note that the cradleincludes a void 1204 through which light passes between the ferrule 1000and the optical device 1022. Thus the reference point 1202 is located inthis void. Generally, the reference points described here and elsewhereare abstract geometric features, and do not need to correspond to aphysical feature (e.g., surface, volume) of the objects that are beingaligned.

In FIG. 13, a perspective view shows a cradle 1302 according to anotherexample embodiment. This cradle 1302 may be used with ferrules describedearlier (e.g., ferrule 1000 shown in FIG. 10) and has a same or similarCTE as the ferrule. The cradle 1302 includes two or more mountingmembers that in this example are configured as hollow prisms 1304 thatextend from a bottom surface 1306 of the cradle 1302. The bottom surface1306 faces a substrate to which the cradle 1302 is bonded.

The cradle 1302 has bonding pads 1308 that are usable with a bondingmaterial that bonds the cradle 1302 to a substrate at a bondingtemperature. The cradle 1302 has a first thermal expansion coefficientand the substrate has a second thermal expansion coefficient differentthan the first thermal expansion coefficient. The mounting members canflex when the cradle 1302 expands or contracts relative to the substratedue to a change in temperature. The hollow prisms 1304 are locatedaround the perimeter of the cradle 1302, and all have the samedimensions. Hollow cylinders may be used instead of or in addition tothe hollow prisms 1304. The prisms 1304 are also symmetrically arrangedaround a reference point 1310 of the cradle 1302 (located in lightpass-thru void 1312). Thus, when the hollow prisms 1304 flex due tothermal expansion, the reference point 1310 will experience minimumdeflection relative to a corresponding reference point of the opticaldevice that is mounted to or part of the substrate. The cradle also hasrecesses 1310 that are used to retain nuts 1026 that mate with screws1024 to hold the top 1022 in place thus retaining the ferrule in thecradle.

In FIGS. 14A-B, bottom and side views shows cradle 1402 according toanother example embodiment. This cradle 1402 may be used with a ferrulethat has a same or similar CTE as the cradle 1402. Generally, thegeometry of the ferrule will be different than previous illustrations,e.g., having a row or array of optical output locations larger in aside-to-side direction 1403 than previously shown. The cradle 1402includes two mounting members that in this example are configured aslegs 1404 that extend from a top surface 1406 of the cradle 1402. Thebottom surface 1412 faces a substrate to which the cradle 1402 isbonded.

The cradle 1402 has bonding pads 1408 that are usable with a bondingmaterial that bonds the cradle 1402 to a substrate at a bondingtemperature. The cradle 1402 has a first thermal expansion coefficientand the substrate has a second thermal expansion coefficient differentthan the first thermal expansion coefficient. The mounting members 1404can flex when the cradle 1402 expands or contracts relative to thesubstrate due to a change in temperature. The mounting members 1404 arelocated on ends of the cradle 1402, and have the same dimensions. Themounting members 1404 are symmetric about a reference point 1410 of thecradle 1402 (located in light pass-thru void 1412). Thus, when thehollow cylinders 1404 flex due to thermal expansion, the reference point1410 will experience minimum deflection relative to a correspondingreference point of the optical device that is mounted to or part of thesubstrate.

In the embodiments described above, geometry of a cradle is designed tominimize displacement of a reference point of a ferrule that is held inthe cradle. Generally, this minimizes the net displacement of aplurality of optical input/output locations of the ferrule relative toan optical device. An example of this is shown in the diagram of FIG.15. A plurality of optical input/output locations 1500 are arranged intotwo rows. A reference point 1502 is centered horizontally at the middleof the rows and centered vertically between the rows. During expansionor contraction of the ferrule, input/output locations 1500 a-d willexperience the greatest displacements, as the distances 1504 a-d of thecenters of these locations is furthest from the reference point 1502. Ifthe reference point 1502 is moved elsewhere, at least one of thedistances 1504 a-d will increase, thus risking greater misalignment forat least one of the input/output locations 1500 a-d than for the others.

Generally, reference point may be chosen to minimize the distance to thefurthest input/output location. This may optionally be applied tonon-symmetric patterns. A non-symmetric arrangement of input/outputlocations 1600 according to an example embodiment is shown in thediagram of FIG. 16. In this case, the reference point 1602 is centeredhorizontally at the middle of the top row and centered verticallybetween the rows. This results in input/output locations 1600 a-c havingthe greatest displacement to expansion/contraction, as the distances1604 a-c of the centers of these locations is furthest from thereference point 1602. In other embodiments, the centroid of a shapeformed by the input/output locations 1600 may be used instead, whichwould shift the reference point slightly to the left and upwards fromwhat is shown here.

In FIG. 17, a flowchart shows a method according to an exampleembodiment. The method involves coupling 1700 an optical ferrule to asubstrate via a cradle at an assembly temperature. The optical ferrulefits loosely within the cradle at the assembly temperature. The opticalferrule has a first thermal expansion coefficient and the cradle has asecond thermal expansion coefficient different than the first thermalexpansion coefficient. One or more devices coupled to the substrate areactivated 1701 such that the substrate, the cradle, and the opticalferrule reach an operating temperature. Relative expansion 1702 of theoptical ferrule and the cradle at the operating temperature cause theone or more output locations of the optical ferrule to be aligned withan optical device attached to the substrate.

In FIG. 18, a flowchart shows a method according to another exampleembodiment. The method involves bonding 1800 two or more bonding pads ofa cradle to a substrate at a bonding temperature. The cradle has two ormore mounting members that mechanically couple the respective two ormore bonding pads to the cradle. The cradle and substrate are caused1801 to reach an assembly temperature. An optical ferrule is inserted1802 into the cradle such that the cradle secures the optical ferrulerelative to an optical device mounted on the substrate. The cradle andsubstrate are caused 1803 to reach an operating temperature. Thedifference between the bonding temperature and the operating temperaturecauses a deformation of the mounting members due to a difference inthermal expansion coefficients between the cradle and the substrate. Thedeformation maintains alignment between the optical device and opticalferrule.

In FIG. 19, a side view shows an optical subassembly according toanother example embodiment. An optical ferrule 1900 and cradle 1902 maybe configured similar to other ferrules described above. The cradle 1902is configured to receive and secure the ferrule 1900 to a substrate 1904such that the ferrule is optically aligned with an optical device 1906at an operating temperature. The cradle 1902 includes a lens 1908configured to modify a light path between the optical ferrule 1900 andthe optical device 1906. Some or all of cradle 1902 may be formed of amaterial that is transparent to wavelengths of light of interest. Thelens 1908 may be a collimating lens that substantially collimates lighttransferred between the optical ferrule 1900 and the optical device1906. Two or more mounting members 1910 mechanically couple the cradle1902 to the substrate 1904. The two or more mounting members 1910reversibly deflect in response to a force applied at an end of themembers 1910 where they are joined with the substrate 1904.

In FIG. 21, a side view shows an optical component 2100 according toanother example embodiment, in which ferrules and cradles describedabove are formed as a single, integral piece. The optical component hasan attachment area 2102 for receiving and permanently attaching aplurality of optical fibers 2104. A light redirecting member 2106receives light along a first direction 2108 from the plurality ofoptical fibers 2102 and redirects the light along a different seconddirection 2110. The redirected light exits the optical component 2100 atexit locations on a mating plane 2112. The exit locations aresubstantially centered on a first alignment plane 2114 normal to thefirst direction.

Two or more bonding pads 2116 are usable with a bonding material thatbonds the optical component 2100 to a substrate 2118 at a bondingtemperature. The component 2100 is formed of a material (e.g.,transparent, optics-grade plastic) a first thermal expansion coefficientand the substrate 2118 has a second thermal expansion coefficientdifferent than the first thermal expansion coefficient. Two or moremounting members 2120 mechanically couple the respective two or morebonding pads 2116 to the component 2100. The two or more mountingmembers 2120 reversibly deflect in response to a force applied betweenthe bonding pad and attachment regions of the two or more mountingmembers to the component 2100, such that the location of theintersection of the first alignment plane 2114 with the substrate 2118is minimally affected by temperature. The optical component 2100 mayinclude a lens 2122 configured to modify a light path between thecomponent and an optical device 2124, the optical device 2124 located onthe substrate 2118.

Additional information regarding connectors that may be used inconjunction with the approaches described herein is provided in thefollowing commonly owned and concurrently filed U.S. patent applicationswhich are incorporated herein by reference: U.S. patent application Ser.No. ______, having the title “Optical Connector” and identified byAttorney Docket Number 70228US002; U.S. patent application Ser. No.______, having the title “Optical Connector with Tilted Mirror” andidentified by Attorney Docket Number 78847US002; U.S. patent applicationSer. No. ______, having the title “Optical Ferrules and Optical FerruleMolds” and identified by Attorney Docket Number 75985US002;

Embodiments described in this disclosure include:

Item 1. An optical ferrule comprising:

an attachment area for receiving and permanently attaching to aplurality of optical fibers;

a light redirecting member for receiving light, along a first direction,from a plurality of fibers received by and permanently attached to theattachment area and redirecting the received light along a differentsecond direction the redirected light exiting the ferrule at exitlocations on a mating plane, the exit locations being substantiallycentered on a first alignment plane normal the first direction;

a pair of first engagement features protruding from opposite lateralsides of the optical ferrule, the first engagement features beingsubstantially centered on the first alignment plane; and

a second engagement feature, different from the pair of first engagementfeatures, protruding from a front side of the optical ferrule, andsubstantially centered on a second alignment plane perpendicular to thefirst alignment plane, the second alignment plane bisecting the exitlocations into substantially equal halves.

Item 2. The optical ferrule of Item 1, wherein the exit locationscomprise a row of optical output locations along the first alignmentplane.Item 3. The optical ferrule of any of Items 1-2, wherein the firstengagement features comprise first and second tabs extending from theopposite lateral sides of the optical ferrule, the first and second tabslocated within respective first and second cavities of a cradle thatsecures the optical ferrule, the first and second cavities constrainingthe two tabs along the first direction when the optical ferrule is fitinto the cradle.Item 4. The optical ferrule of Item 3, further comprising first andsecond lateral clearances between the first and second tabs and therespective first and second cavities such that the tab can displace in alateral direction, wherein there is little or no clearance between thefirst and second tabs and the respective first and second cavities inthe first direction.Item 5. The optical ferrule of any of Items 1-4, wherein the secondengagement feature comprises a tab extending from the front side, thetab being placed in a cavity of a cradle configured to secure theferrule.Item 6. The optical ferrule of Item 5, further comprising a clearancebetween the tab and the cavity such that the tab can displace in thefirst direction, wherein there is little or no clearance between thefirst and second tabs and the respective first and second cavities inthe lateral direction.Item 7. The optical ferrule of any of Items 1-6, wherein the opticalferrule is formed of a polymer.Item 8. The optical ferrule of any of Items 1-7, further comprising amating surface that optically interfaces with an optical device on asubstrate.Item 9. The optical ferrule of any of Items 1-8, wherein the opticalferrule is configured to loosely fit into a cradle at an assemblytemperature and to tightly fit into the cradle at an operatingtemperature.Item 10. The optical ferrule of Item 9, wherein the assembly temperatureis lower than the operating temperature.Item 11. An optical ferrule, comprising:

an attachment end configured to receive and secure an optical waveguide;

a distal tip opposed to the attachment end along a longitudinaldirection;

a light redirecting element configured to redirect light between theoptical waveguide and a mating surface of the optical ferrule;

a longitudinal constraint member operable to interface with acorresponding longitudinal constraint member of a cradle that receivesand secures the optical ferrule; and

a side-to-side constraint member operable to interface with acorresponding side-to-side constraint member of the cradle, wherein thelongitudinal and side-to-side constraint members minimize displacementof a reference point of the optical ferrule relative to a correspondingreference point of the cradle due to different thermal expansioncoefficients of the optical ferrule and the cradle causing a change insize of the optical ferrule relative to the cradle in response to achange of temperature.

Item 12. The optical ferrule of Item 11, wherein the mating surfacecomprises a row of optical output locations along a side-to-side line,the reference point being at a center of the side-to-side line.Item 13. The optical ferrule of Item 12, wherein the longitudinalconstraint member comprises two tabs extending from opposing sides ofthe optical ferrule and aligned with the side-to-side line, thecorresponding longitudinal constraint members of the cradle comprisingtwo cavities that respectively constrain the two tabs longitudinally andallow side-to-side displacement of the two tabs when the optical ferruleis fit into the cradle.Item 14. The optical ferrule of any of Items 12-13, wherein theside-to-side constraint member comprises a tab extending from the distaltip aligned with the center of the side-to-side line, the correspondingside-to-side constraint member comprising a cavity that constrainsside-to-side displacement of the tab and allows longitudinaldisplacement of the tab when the optical ferrule is fit into the cradle.Item 15. The optical ferrule of any of Items 11-14, wherein a firstthermal coefficient of expansion of the optical ferrule is larger than asecond thermal coefficient of expansion of the cradle.Item 16. The optical ferrule of Item 15, wherein the optical ferrule isformed of a polymer.Item 17. The optical ferrule of any of Items 11-16, wherein the matingsurface is operable to optically interface with an optical device on asubstrate, wherein the cradle aligns the optical ferrule with theoptical device.Item 18. The optical ferrule of any of Items 11-17, wherein the opticalferrule is configured to loosely fit into the cradle at an assemblytemperature and to tightly fit into the cradle at an operatingtemperature.Item 19. The optical ferrule of Item 18, wherein the assemblytemperature is lower than the operating temperature.Item 20. A cradle configured to receive and secure an optical ferrule,the cradle comprising:

a corresponding longitudinal constraint member operable to interfacewith a longitudinal constraint member of the optical ferrule; and

a corresponding side-to-side constraint member operable to interfacewith a side-to-side constraint member of the optical ferrule, whereinthe longitudinal and side-to-side constraint members minimizedisplacement of a reference point of a mating surface of the opticalferrule with a corresponding reference point of the cradle due to achange in size of the optical ferrule relative to the cradle, the changein size being induced by different thermal expansion coefficients of theoptical ferrule and the cradle and a change in temperature.

Item 21. The cradle of Item 20, wherein the mating surface comprises arow of optical output locations along a side-to-side line, the referencepoint being at a center of the side-to-side line.Item 22. The cradle of Item 21, wherein the longitudinal constraintmember of the optical ferrule comprises two tabs extending from opposingsides of the optical ferrule and aligned with the side-to-side line, thecorresponding longitudinal constraint members of the cradle comprisingtwo cavities that respectively constrain the two tabs and allowside-to-side displacement of the two tabs when the optical ferrule isfit into the cradle.Item 23. The cradle of any of Items 21-22, wherein the side-to-sideconstraint member comprises a tab extending from a distal tip of theoptical ferrule that is aligned with the center of the side-to-side lineand the corresponding side-to-side constraint member comprises a cavitythat constrains side-to-side displacement of the tab and allowslongitudinal displacement of the tab when the optical ferrule is fitinto the cradle.Item 24. The cradle of any of Items 20-23, wherein a first thermalcoefficient of expansion of the optical ferrule is larger than a secondthermal coefficient of expansion of the cradle.Item 25. The cradle of Item 24, wherein the cradle is formed of aceramic.Item 25a. The cradle of Item 24 where the cradle is formed of silica.Item 26. The cradle of any of Items 20-25a, wherein the cradle alignsand secures the optical ferrule to a substrate such that the matingsurface optically interfaces with an optical device on the substrate.Item 27. The cradle of any of Items 20-26, wherein the optical ferruleis configured to loosely fit into the cradle at an assembly temperatureand to tightly fit into the cradle at an operating temperature.Item 28. The cradle of Item 27, wherein the assembly temperature islower than the operating temperature.Item 28a. The cradle of any of Items 20-28, further comprising a lensconfigured to modify a light path between the optical ferrule and anoptical device, the optical device located on a substrate to which thecradle is attached.Item 28b. The cradle of Item 28a, wherein the lens comprises acollimating lens.Item 28c. The cradle of any of Items 20-28b, further comprising secondcorresponding longitudinal and side-to-side constraint membersconfigured to minimize a second displacement of a second reference pointof a second optical ferrule with a corresponding second reference pointof the cradle due to a change in size of the second optical ferrulerelative to the cradle.28d. The cradle of any of Items 20-28c, further configured to receiveand secure two or more ferrules.Item 29. An optical assembly, comprising:

an optical ferrule comprising a light redirecting element configured toredirect light between an optical waveguide and a mating surface of theoptical ferrule, the optical ferrule having a first thermal expansioncoefficient; and

a cradle configured to hold and secure the optical ferrule to asubstrate, the cradle having a second thermal expansion coefficientdifferent than the first thermal expansion coefficient, wherein theoptical ferrule is configured to fit loosely within the cradle at anassembly temperature and to expand into the cradle at an operatingtemperature.

Item 30. The optical assembly of Item 29, wherein the optical ferrulecomprises at least one constraint member and the cradle comprises atleast one corresponding constraint member, the constraint member andcorresponding constraint member interfacing such that a displacementbetween a reference point of the optical ferrule and a correspondingreference point of the cradle is minimized between the assemblytemperature and the operating temperature.Item 31. The optical assembly of Item 30, wherein the optical ferrulecomprises a row of optical output locations arranged in a side-to-sideline along the mating surface, the reference point being at a center ofthe side-to-side line.Item 32. The optical assembly of any of Items 29-30, wherein the atleast one constraint member comprises a longitudinal constraint memberand a side-to-side constraint member, and the at least one correspondingconstraint member comprises a corresponding longitudinal constraintmember that interfaces with the longitudinal constraint member and acorresponding side-to-side constraint member that interfaces with theside-to-side longitudinal constraint member.Item 33. The optical assembly of Item 32, further comprising aside-to-side clearance between the longitudinal constraint member andthe corresponding longitudinal constraint member such that thelongitudinal constraint member can displace in a side-to-side direction,and wherein there is little or no clearance between the longitudinalconstraint member and the corresponding longitudinal constraint memberin a longitudinal direction.Item 34. The optical assembly of any of Items 29-33, wherein theassembly temperature is lower than the operating temperature.Item 35. The optical assembly of any of Items 29-34, wherein the opticalferrule is formed of a polymer and the cradle is formed of a ceramic.Item 36. The optical assembly of any of Items 29-35, further comprisingan optical device attached to the substrate, the cradle aligning one ormore optical output locations of the optical ferrule with the opticaldevice.Item 37. The optical assembly of Item 36, wherein at least part of theone or more optical output locations are misaligned with the opticaldevice at the assembly temperature and the one or more optical outputlocations are optimally aligned with the optical device at the operatingtemperature.Item 37a. The optical assembly of any of Items 29-37, wherein the cradlefurther comprises a lens configured to modify a light path between theoptical ferrule and an optical device, the optical device located on thesubstrate.Item 37b. The optical assembly of Item 37a, wherein the lens comprises acollimating lens.Item 37c. The optical assembly of any of Items 29-37b, wherein thecradle is further configured to hold and secure a two or more opticalferrules to a substrate.Item 37d. The optical assembly of any of Items 29-37c, wherein thecradle and the optical ferrule are formed integrally.Item 38. A method, comprising:

coupling an optical ferrule to a substrate via a cradle at an assemblytemperature, the optical ferrule fitting loosely within the cradle atthe assembly temperature, the optical ferrule having a first thermalexpansion coefficient and the cradle having a second thermal expansioncoefficient different than the first thermal expansion coefficient; and

activating one or more devices coupled to the substrate such that thesubstrate, the cradle, and the optical ferrule reach an operatingtemperature, wherein relative expansion of the optical ferrule and thecradle at the operating temperature cause the one or more outputlocations of the optical ferrule to be aligned with an optical deviceattached to the substrate.

Item 38a. The method of Item 38, wherein the relative expansion of theoptical ferrule and the cradle at the operating temperature causes theoptical ferrule to fit tightly within the cradle.Item 39. The method of any of Items 38-38a, further comprisingtransferring light between the optical ferrule and the optical devicevia the one or more output locations at a mating surface of the opticalferrule at the operating temperature.Item 40. The method of Item 39, wherein transferring light between theoptical ferrule and the optical device comprises redirecting lightbetween the mating surface and an optical waveguide coupled to an end ofthe optical ferrule.Item 41. The method of Item 40, further comprising minimizing adisplacement between a reference point of the optical ferrule and acorresponding reference point of the cradle between the assemblytemperature and the operating temperature.Item 42. The method of Item 41, wherein the displacement is minimizedvia:

at least one longitudinal constraint member of the optical ferrule thatinterfaces with at least one corresponding longitudinal constraintmember of the cradle; and

at least one side-to-side constraint member of the optical ferrule thatinterfaces with at least one corresponding side-to-side constraintmember of the cradle.

Item 43. A cradle configured to receive and secure an optical ferrule,the cradle comprising:

a restraining member configured to restrain the optical ferrule; and

two or more bonding pads usable with a bonding material that bonds thecradle to a substrate at a bonding temperature, the cradle having afirst thermal expansion coefficient and the substrate having a secondthermal expansion coefficient different than the first thermal expansioncoefficient; and

two or more mounting members that mechanically couple the respective twoor more bonding pads to the cradle, the two or more mounting membersreversibly deflecting in response to a force applied between the bondingpad and attachment regions of the two or more mounting members to thecradle, the force due to the different first and second expansioncoefficients.

Item 44. The cradle of Item 43, wherein the two or more mounting memberscomprises two or more legs affixed near a top surface of the cradle thatis opposed to the two more bonding pads.Item 45. The cradle of Item 44, wherein the two or more legs comprisefour or more legs each affixed at a different corner of the cradle.Item 46. The cradle of any of Items 44-45, wherein the two or more legscomprise three or more legs each affixed at a different edge of thecradle.Item 47. The cradle of any of Items 43-46, wherein the two or moremounting members comprises two or more hollow cylinders or hollow prismsthat extend from a bottom surface of the cradle that faces thesubstrate.Item 48. The cradle of any of Items 43-47, wherein the two or moremounting members are symmetrically arranged relative to the cradle suchthat the reversible deflection minimizes displacement of a referencepoint of the optical ferrule relative to a corresponding reference pointof the substrate.Item 49. The cradle of Item 48, wherein the displacement is minimizedwhen the cradle expands or contracts relative to the substrate due to achange in temperature.Item 49a. The cradle of any of Items 43-49, further comprising a lensconfigured to modify a light path between the optical ferrule and anoptical device, the optical device located on a substrate to which thecradle is attached.Item 49b. The cradle of Item 49a, wherein the lens comprises acollimating lens.Item 50. A cradle configured to receive and secure an optical ferrule,the cradle comprising:

a restraining member configured to restrain the optical ferrule; and

two or more bonding pads with a bonding material that bonds the cradleto a substrate at the bonding temperature, the cradle having a firstthermal expansion coefficient and the substrate having a second thermalexpansion coefficient different than the first thermal expansioncoefficient; and

two or more mounting members that mechanically couple the respective twoor more bonding pads to the cradle, the two or more mounting membersdeformable in response to expansions of the cradle relative to thesubstrate, the relative change in expansions due to a change between abonding temperature and an operating temperature, the two or moremounting members deformable such that the cradle maintains an alignmentbetween the optical ferrule and an optical device attached to thesubstrate at least at the operating temperature.

Item 51. The cradle of Item 50, wherein the two or more mounting memberscomprises two or more legs affixed near a top surface of the cradle thatis opposed to the two more bonding pads.Item 52. The cradle of Item 51, wherein the two or more legs comprisefour or more legs each affixed at a different corner of the cradle.Item 53. The cradle of any of Items 51-52, wherein the two or more legscomprise three or more legs each affixed at a different edge of thecradle.Item 54. The cradle of any of Items 50-53, wherein the two or moremounting members comprises two or more hollow cylinders or hollow prismsthat extend away from a bottom surface of the cradle that faces thesubstrate.Item 55. The cradle of any of Items 50-54, wherein the two or moremounting members are symmetrically arranged relative to the cradle suchthat the reversible deflection minimizes displacement of a referencepoint of the optical ferrule relative to a corresponding reference pointof the substrate.Item 56. The cradle of Item 55, wherein the displacement is minimizedwhen the cradle expands or contracts relative to the substrate due to achange in temperature.Item 56a. The cradle of any of Items 50-56, further comprising a lensconfigured to modify a light path between the optical ferrule and theoptical device.Item 56b. The cradle of Item 56a, wherein the lens comprises acollimating lens.Item 57. A method, comprising:

bonding two or more bonding pads of a cradle to a substrate at a bondingtemperature, the cradle comprising two or more mounting members thatmechanically couple the respective two or more bonding pads to thecradle;

causing the cradle and substrate to reach an assembly temperature, thedifference between the bonding temperature and the assembly temperaturecausing a deformation of the mounting members due to a difference inthermal expansion coefficients between the cradle and the substrate; and

inserting an optical ferrule into the cradle such that the cradlesecures the optical ferrule relative to an optical device mounted on thesubstrate.

Item 58. The method of Item 57, further comprising activating one ormore devices coupled to the substrate such that the substrate, thecradle, and the optical ferrule reach an operating temperature, whereinexpansion of the cradle relative to the substrate at the operatingtemperature brings the optical ferrule into alignment with the opticaldevice.Item 59. The method of Item 58, further comprising transferring lightbetween the optical ferrule and the optical device via the one or moreoutput locations at a mating surface of the optical ferrule at theoperating temperature.Item 60. The method of Item 59, wherein transferring light between theoptical ferrule and the optical device comprises redirecting lightbetween the mating surface and an optical waveguide coupled to an end ofthe optical ferrule.Item 61. An optical component comprising:

an attachment area for receiving and permanently attaching a pluralityof optical waveguides;

a light redirecting member for receiving light along a first directionfrom a plurality of optical fibers received by and permanently attachedto the attachment area and redirecting the light along a differentsecond direction, the redirected light exiting the ferule at exitlocations on a mating plane, the exit locations being substantiallycentered on a first alignment plane normal the first direction;

two or more bonding pads usable with a bonding material that bonds thecomponent to a substrate at a bonding temperature, the component havinga first thermal expansion coefficient and the substrate having a secondthermal expansion coefficient different than the first thermal expansioncoefficient; and

two or more mounting members that mechanically couple the respective twoor more bonding pads to the component, the two or more mounting membersreversibly deflecting in response to a force applied between the bondingpad and attachment regions of the two or more mounting members to thecomponent, such that the location of the intersection of the firstalignment plane with the substrate is minimally affected by temperature.

Item 62. The optical assembly of Item 61, wherein the component furthercomprises a lens configured to modify a light path between the componentand an optical device, the optical device located on the substrate.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The use of numerical ranges by endpointsincludes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, and 5) and any range within that range.

Various modifications and alterations of the embodiments discussed abovewill be apparent to those skilled in the art, and it should beunderstood that this disclosure is not limited to the illustrativeembodiments set forth herein. The reader should assume that features ofone disclosed embodiment can also be applied to all other disclosedembodiments unless otherwise indicated. It should also be understoodthat all U.S. patents, patent applications, patent applicationpublications, and other patent and non-patent documents referred toherein are incorporated by reference, to the extent they do notcontradict the foregoing disclosure.

1. An optical ferrule comprising: an attachment area for receiving andpermanently attaching to a plurality of optical fibers; a lightredirecting member for receiving light, along a first direction, from aplurality of fibers received by and permanently attached to theattachment area and redirecting the received light along a differentsecond direction the redirected light exiting the ferrule at exitlocations on a mating plane, the exit locations being substantiallycentered on a first alignment plane normal the first direction; a pairof first engagement features protruding from opposite lateral sides ofthe optical ferrule, the first engagement features being substantiallycentered on the first alignment plane; and a second engagement feature,different from the pair of first engagement features, protruding from afront side of the optical ferrule, and substantially centered on asecond alignment plane perpendicular to the first alignment plane, thesecond alignment plane bisecting the exit locations into substantiallyequal halves.
 2. The optical ferrule of claim 1, wherein the firstengagement features comprise first and second tabs extending from theopposite lateral sides of the optical ferrule, the first and second tabslocated within respective first and second cavities of a cradle thatsecures the optical ferrule, the first and second cavities constrainingthe two tabs along the first direction when the optical ferrule is fitinto the cradle, wherein the optical ferrule further comprises first andsecond lateral clearances between the first and second tabs and therespective first and second cavities such that the tab can displace in alateral direction, and wherein there is little or no clearance betweenthe first and second tabs and the respective first and second cavitiesin the first direction.
 3. An optical ferrule, comprising: an attachmentend configured to receive and secure an optical waveguide; a distal tipopposed to the attachment end along a longitudinal direction; a lightredirecting element configured to redirect light between the opticalwaveguide and a mating surface of the optical ferrule; a longitudinalconstraint member operable to interface with a correspondinglongitudinal constraint member of a cradle that receives and secures theoptical ferrule; and a side-to-side constraint member operable tointerface with a corresponding side-to-side constraint member of thecradle, wherein the longitudinal and side-to-side constraint membersminimize displacement of a reference point of the optical ferrulerelative to a corresponding reference point of the cradle due todifferent thermal expansion coefficients of the optical ferrule and thecradle causing a change in size of the optical ferrule relative to thecradle in response to a change of temperature.
 4. A cradle configured toreceive and secure an optical ferrule, the cradle comprising: acorresponding longitudinal constraint member operable to interface witha longitudinal constraint member of the optical ferrule; and acorresponding side-to-side constraint member operable to interface witha side-to-side constraint member of the optical ferrule, wherein thelongitudinal and side-to-side constraint members minimize displacementof a reference point of a mating surface of the optical ferrule with acorresponding reference point of the cradle due to a change in size ofthe optical ferrule relative to the cradle, the change in size beinginduced by different thermal expansion coefficients of the opticalferrule and the cradle and a change in temperature. 5-10. (canceled) 11.The optical ferrule of claim 1, wherein the exit locations comprise arow of optical output locations along the first alignment plane.
 12. Theoptical ferrule of claim 1, wherein the second engagement featurecomprises a tab extending from the front side, the tab being placed in acavity of a cradle configured to secure the ferrule.
 13. The opticalferrule of claim 12, further comprising a clearance between the tab andthe cavity such that the tab can displace in the first direction,wherein there is little or no clearance between the first and secondtabs and the respective first and second cavities in the lateraldirection.
 14. The optical ferrule of claim 1, wherein the opticalferrule is formed of a polymer.
 15. The optical ferrule of claim 1,further comprising a mating surface that optically interfaces with anoptical device on a substrate.
 16. The optical ferrule of claim 1,wherein the optical ferrule is configured to loosely fit into a cradleat an assembly temperature and to tightly fit into the cradle at anoperating temperature.
 17. The optical ferrule of claim 16, wherein theassembly temperature is lower than the operating temperature.
 18. Theoptical ferrule of claim 3, wherein the mating surface comprises a rowof optical output locations along a side-to-side line, the referencepoint being at a center of the side-to-side line.
 14. The opticalferrule of claim 18, wherein the longitudinal constraint membercomprises two tabs extending from opposing sides of the optical ferruleand aligned with the side-to-side line, the corresponding longitudinalconstraint members of the cradle comprising two cavities thatrespectively constrain the two tabs longitudinally and allowside-to-side displacement of the two tabs when the optical ferrule isfit into the cradle.
 15. The optical ferrule of claim 18, wherein theside-to-side constraint member comprises a tab extending from the distaltip aligned with the center of the side-to-side line, the correspondingside-to-side constraint member comprising a cavity that constrainsside-to-side displacement of the tab and allows longitudinaldisplacement of the tab when the optical ferrule is fit into the cradle.16. The optical ferrule of claim 3, wherein a first thermal coefficientof expansion of the optical ferrule is larger than a second thermalcoefficient of expansion of the cradle.
 17. The optical ferrule of claim16, wherein the optical ferrule is formed of a polymer.
 18. The opticalferrule of claim 3, wherein the mating surface is operable to opticallyinterface with an optical device on a substrate, wherein the cradlealigns the optical ferrule with the optical device.
 19. The opticalferrule of claim 3, wherein the optical ferrule is configured to looselyfit into the cradle at an assembly temperature and to tightly fit intothe cradle at an operating temperature.
 20. The optical ferrule of claim19, wherein the assembly temperature is lower than the operatingtemperature.
 21. The cradle of claim 4, wherein the longitudinalconstraint member of the optical ferrule comprises two tabs extendingfrom opposing sides of the optical ferrule and aligned with theside-to-side line, the corresponding longitudinal constraint members ofthe cradle comprising two cavities that respectively constrain the twotabs and allow side-to-side displacement of the two tabs when theoptical ferrule is fit into the cradle.